This invention was conceived in the course of a grant from the National Heart and Lung Institute.
Peripheral nerves constitute communication lines in the body of humans and animals. As such, they serve both effector and reporting functions in a multitude of biologic control systems, voluntary as well as involuntary. It is therefore highly desirable to measure the activities in nerves, particularly in intact nerves, both for diagnostic purposes and as a research tool. However, in the past, bioelectric interferences, for example such as cardio-electric interference, present a problem when recording the activity in intact nerves. That is, an intact nerve has both ends of the isolated nerve segment to be measured attached to the body, and any extraneous potentials between the two points of attachment will be seen by a conventional electrode probe of the standard bipolar configuration. Typically, the potentials recorded from the surface of a multifiber, postganglionic, cardiac sympathetic nerve are in the range of one to ten microvolts in amplitude, peak to peak. If the nerve is left intact, and a conventional pair of electrode wires, for example four mm. or more apart, is placed under the isolated nerve segment, the many times larger electric fields of cardiac origin (ECG), will swamp the measurement.
Experimentally, in order to avoid bioelectric interference, the usual procedure is to create a one point attachment by severing the nerve, thus eliminating the extraneous field gradient along the nerve. However, in certain situations, it is mandatory or highly desirable that the nerve in question not be severed, but left intact such as:
1. Long-term nerve monitoring by means of implanted electrodes necessitates an intact nerve if impulse conduction is to be maintained;
2. Diagnostic nerve monitoring in humans, for example during surgery, should be atraumatic;
3. Experimentally, it is undesirable to sever the nerve as (a) this may alter the system under study, for example the measured target organ function, and (b) it may be desirable to record simultaneously both efferent and afferent traffic signals within the same nerve, particularly when these nerve activities are interdependent.
The present method and apparatus is directed to improvements in measuring and recording activities in intact nerves by achieving a nulling of extraneous bioelectric fields.